Ferrous base alloys containing boron



United States Patent 3,212,884 FERROUS BASE ALLOYS CONTAINING BORON Gilbert Soler, deceased, late of Pittsburgh, Pa., by Marjorie 0. Soler, executrix, Columbus, Ohio, and Hyman Freeman, Pittsburgh, and Kenneth Metcalfe, Bridgeville, Pa.

No Drawing. Continuation of application Ser. No. 598,520, July 8, 1956. This application July 3, 1963, Ser. No. 293,238

3 Claims. (Cl. 75-124) This application is a continuation of Serial No. 598,520, filed July 18, 1956 and now abandoned.

Alloys of the type referred to are used for parts in jet engines for aircraft, gas turbines and other high temperature applications where it is necessary to have consistently high strength properties. Each of such engines is made up of a great many individual parts fabricated from the high temperature alloy. The failure of any single part can result in the failure of the entire engine.

Increased use of alloys having high strength at elevated temperatures has developed requirements that specify minimum strength as determined by the stress rupture life of the material. Some commercially produced alloys of this type gave very erratic stress rupture properties with many values below those acceptable for the application. It was not unusual to obtain extremely low as well as acceptable stress rupture properties on products from the same heat, thus making the application of such material questionable. In fact, where such varying results were obtained, the entire heat was scrapped rather than to apply questionable material for such critical use. The necessary rejection of the material having such variable stress rupture properties resulted in low yields of product and reduced production making'it extremely difiicult to meet delivery requirements.

Typical specifications for alloys used in the high temperature applications described require a minimum stress rupture life of 23 hours at a temperature of 1200 F. and loads varying from 60,000 to 65,000 pounds per square inch. In many cases, they also require that the stress rupture life of a notched test specimen exceed that of a smooth test specimen, i.e., thematerial should not be notched sensitive.

An object of this invention, therefore, is to provide an alloy composition which possesses consistently high minimum strength at elevated temperatures.

A further object of this invention is to provide an alloy which has improved notch ductility at elevated temperatures as determined by values obtained from notched stress rupture specimens.

' Another object is to provide an alloy having consistent stress rupture properties and which can be melted commercially and wrought by commercial practices.-

Other objects of this invention will be apparent to those skilled in the art from the following description.

It has been discovered that the stress rupture properties of ferrous base alloys are improved and made more consistent by the presence of definite amounts of boron. In the alloys of this invention having a definite boron content, low stress rupture properties are avoided. Alloys of our invention are precipitation hardenable by-heat treatment alone and do not require any special processing such as hot cold-working to bring about the desirable properties.

In many cases, it is not possible to make a use of hot cold-working to achieve the high strength because of the shape and nature of the finished part.

It has been discovered that improved and consistent stress rupture properties can be obtained in ferrous base alloys containing 20 to 40% nickel, 10 to 25% chromium and 0.0006 to 0.0045% boron when the alloys contain a critical minimum percentage of titanium neces sary for causing nickel-titanium compounds to precipitate after proper heat treatment. From the experience of the inventors, this minimum content of titanium in the alloys of our invention appears to be about 1.35%. In the absence of a critical amount of titanium, the nickel-titanium compounds do not precipitate upon aging.

Ferrous base alloys according to the present invention contain nickel, chromium, titanium and boron within the following ranges:

Ni 20 to 40%.

Cr 10 to 25% Ti 1.35 to 3.0%.

B 0.0010 to 0.0045%.

In addition to these elements, the alloy may contain from 0.02 to 0.10% carbon from 0.10 to 0.35% aluminum, from 0 to 2% manganese, from 0 to 1.50% silicon, from 0.50 to 4.0% molybdenum or from 0.50 to 8. 0% tungsten or both molybdenum and tungsten within these ranges, from 0.10 to 0.50% vanadium, up to 2.0% zirconium, up to 5.0% niobium and up to 5.0% tantalum. The balance is substantially all iron although other elements not inconsistent with the properties desired may be present.

T he alloys can be melted using normal practices in any of the usual production type furnaces such as the electric arc, induction or vacuum or inert gas furnace. They are processed using regular production methods to reduce to intermediate product such as bars, wire, sheet, strip, etc., as well as for fabricating into shapes by machining, forging or other methods.

Improved and consistent stress rupture properties and other properties of the alloys are obtained by giving a suitable heat treatment to the product in finished form. Generally, the alloy is heated to a temperature sufiiciently high to dissolve the intermetallic compounds present and is then quenched. it is reheated at a temperature and for a time necessary to harden it by reprecipitation of the compounds and is thereafter cooled. The temperatures and times employed will vary somewhat depending upon the particular composition of the alloy being heat treated. A preferred hardening treatment is to treat the material at a temperature of about 1800 F. for one hour to dissolve the intermetallic compounds present and then quench. The alloy is then reheated at 1325 F. for 16 hours to cause reprecipitation of the nickel-titanium compounds and is thereafter cooled in air. This specific heat treatment was applied to an alloy of the following composition:

' Percent Percent Ni 25.38 Mn 1.53 Cr -4 14.97 Si .68 .Ti 2.23 Mo 1.26 B 0.0022 V .25

C .066 1% Balance Al .27

Patented Oct. 19, 1965 3 4 This alloy, when tested at 1200 F. under a load of 62,500 The stress rupture properties of alloys of this invention poundsper square inch using notched specimens, gave are given in Tables I and II. Stress rupture properties of Stress rupture P p as follows! alloys not made in accordance with this invention are Hours to Rupture: 815.0 803.6 762.7 655.3 given in Tables III and IV.

Table l OUR ALLOY HAVING A DEFINITE BORON CONTENT [Test Conditions: Temperature, 1200 F.; Load, 65,000 p.s.i.]

Stress rupture life in hours Alloy Boron Notched specimen 7 Smooth specimen N 0. content No.0f Minimum Maximum No.01 Minimum Maximum tests value value tests value value C Mn Si N 1 C1 Ti V Al M0 Table II OUR ALLOY HAVING A DEFINITE BORON CONTENT [Test Conditions: Temperature, 1200 F.; Load, 62,500.p.s.i.]

Stress rupture life in hours Alloy Boron Notched specimen Smooth specimen No. content No. of Minimum Maximum No. of Minimum Maximum tests value value tests value value LLLLLLLLLLLLLI value Smooth specimen Stress rupture life in hours value L L2 L2 L1 1 2 L L 2 value Smooth specimen tests Table III ANALYSES OF ALLOYS value LLLLLLLLLLLLLL 037221455444 12 2 .QLLLL-L 1 l M ANALYSES OF ALLOYS Notched specimen No.0! Minimum Maximum No.0i Minimum Maximum tests MnSi'Ni Stress rupture life in hours value Table IV value 13201769 0 LL L5 3 5 3 Notched specimen No. of Minimum Maximum No.0! Minimum Maximum tests [Test Conditions: Temperature, 1200 F.; Load, 65,000 p.s.i.]

Alloy No.

OUR ALLOY HAVING NO DEFINIIE BORON CONTENT Boron content ALLOYS HAVING NO DEFINITE BORON CONTENT [Test Conditions: Temperature, 1200 F.; Load, 62,500 p.s.i.]

Alloy Alloy No.

Alloy ANALYSES OF ALLOYS Alloy N 0 Mn S1 N1 C1 Ti V A1 M0 The plus sign after some values in the tables indicates that the test was not carried to failure of the specimen for it is common practice to discontinue the test after the specimen has been under load for a period of time that considerably exceeds the required hours to rupture. Such values would be expected to be greater if the tests had been allowed to continue to failure. However, since. they are well above the requirements, discontinuing the tests makes testing equipment available.

The material on which the tests in all of the tables were made was produced in commercial size furnaces, the heats weighing from 5 to 13 tons each.

The values in all of the tables were obtained on specimens which had been precipitation hardened.

Table I gives the stress rupture properties of alloys of our invention having a definite boron content and tested at a temperature of 1200 F. using a load of 65,000 pounds per square inch.

Table II gives the stress rupture properties of alloys of our invention having a definite boron content and tested at a temperature of 1200 F. using a load of 62,500 pounds per square inch.

Table III gives the stress rupture properties of alloys having no definite boron content and tested at a temperature of 1200 F. using a load of 65,000 pounds per square inch.

Table IV gives the stress rupture properties of alloys having no definite boron content and tested at a temperature of 1200 F. using a load of 62,500 pounds per square inch.

Each table gives values for the notched and the smooth type of specimen.

Comparison of the minimum values of Tables I and II with the minimum values in Tables III and IV shows the.

improved stress rupture properties obtainable in alloys of this invention having a definite boron content.

The alloy of this invention is less notch sensitive than an alloy having no definite boron content, forv example, Alloy 5 in Table I containing .0017 boron has a minimum value of 76.6 hours on a notched specimen and a minimum value of 60.3 hours on a smooth specimen, the notched specimen value exceeding the smooth specimen value. Alloy e in Table. III containing less than .0006 boron has a minimum value of 3.2 hours on a notched specimen and a minimum value of 21.1 hours on a smooth specimen indicating that this alloy is notch sensitive.

The microstructure of alloys according to the invention, which have been solution treated and aged, consists of fine grains of equiaXed austenite having a precipitate of fine patricles of nickel-titanium compounds throughout its structure. Such structure is only obtained'when the alloy contains sufficient titanium to cause reprecipitation of the nickel-titanium compounds during the aging treatment.

We claim:

1. A ferrous base alloy consisting essentially of 2 0 to 40% nickel, 10 to 25% chromium, 1.35 to 3.0% titanium, 0.0010 to 0.0045% boron, 0.02 to 0.10% carbon, 0.10 to 0.35% aluminum, up to 2.0% manganese, up to 1.50% silicon, at least one member of the group consisting of molybdenum and tungsten, the molybdenum being from 0.50 to 4.0%, the tungsten being from 0.50 to 8.0%, 0.10 to 0.50% vanadium, up to 2.0% zirconium, up to 5.0% niobium and up to 5.0% tantalum, the balance being iron.

2. A precipitation hardened ferrous base alloy of the composition claimed in claim 1.

3. A ferrous base alloy of the composition claimed in claim 1 which has been precipitation hardened; in the absence of hot cold-working.

References Cited by the Examiner UNITED STATES PATENTS 11/62 Aggen l24 

1. A FERROUS BASE ALLOY CONSISTING ESSENTIALLY OF 20 TO 40% NICKEL, 10 TO 25% CHROMIUM, 1.35 TO 3.0% TITANIUM, 0.0010 TO 0.0045% BORON, 0.02 TO 0.10% CARBON, 0.10 TO 0.35% ALUMINUM, UP TO 2.0% MANGANESE, UP TO 1.50% SILICON, AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN, THE MOLYBDENUM BEING FROM 0.50 TO 4.0%, THE TUNGSTEN BEING FROM 0.50 TO 8.0%, 0.10 TO 0.50% VANADIUM, UP TO 2.0% ZIRCONIUM, UP TO 5.0% NIOBIUM AND UP TO 5.0% TANTALUM, THE BALANCE BEING IRON. 